Preparing a surface for painting is often more work than the actual job of painting. For paint to adhere, surfaces generally have to be dirt free, dust free, dog hair free, crayon free, fingerprint free, paint chip free, oil and grease free, mold and mildew free, and free of anything else that could possibly interfere with the paint staying on...
The only thing that's not free is the paint and cleaning supplies you have to buy.
Many surfaces that look hopelessly impossible to prepare can be cleaned thoroughly by power washing with a pressure washer. "The best cleaning job will give you the longest-lasting paint job" said Andy - Chicago Painting Contractors
Power washing with a pressure washer and the necessary chemicals will give you the debris-free clean you need. However, before you start planning to hose down the house, plan your power washing and painting schedule to allow for drying time. Power washing may only take a few hours, but it can take days for outdoor siding, roofs, decks, furnishings or masonry work to dry.
Start your power washing project by sweeping, vacuuming, or brushing off the loose debris on the surface area. By doing so, you'll allow the chemicals and the pressure from the washer to work more effectively. Then check for stains such as oil and mildew – these will require chemical treatment. (A solution of 3 parts water to 1 part bleach will kill mildew.) Depending on the size and location of the stains, you can spot-treat the stains by hand, or you can apply the stain solution with the pressure washer or a garden sprayer.
Before you start spraying, take notice of where seepage may occur. Areas around window and door frames and vents will be susceptible to leakage. (Do not power spray windows or they may break.) Make sure you won't be spraying any overhead or in-ground electrical lines. Take time to cover electrical outlets, outdoor equipment, and sensitive plants. According to Chicago House Painters if you're spraying on a bleach solution, cover everything in the vicinity to keep away unwanted bleach stains. If you're spraying off loose paint, putting a tarp down will help cleanup. (It will also help to let the kids stay at a friend's house. You don't want them taking an outdoor shower in bleach and lead paint.)